1. Field of the Invention
The present invention relates to a device for measuring various quantities concerning a flow, among others, relates to a flow rate and flow velocity measurement device using a detection element integrally formed on a support body and/or a temperature sensitive semiconductor chip, and relates to a measurement device suitably applied, for example, as a combustion controlling mass flow rate sensor of an engine for a vehicle or industry, or a mass flow rate sensor for an industrial air conditioning system and compressor pressurized air supply system and, furthermore, an air/fuel ratio controlling flow rate sensor of a domestic gas hotplate.
2. Description of the Related Art Japanese patent application laid-open No. 9-503311 proposes xe2x80x9cA sensor support body for a device measuring an intake of internal combustion engine, provided with a sensor support body and a sensor element on a plate inserted into a flow rate medium, wherein the sensor element has at least one measurement resistor concerned with temperature, and the sensor element is accommodated in a notch of the sensor support body while forming approximately the same face as the sensor support bodyxe2x80x9d. Further, in an embodiment of the same gazette xe2x80x9cThe sensor element has a plate-like shape, and its largest surface is lined up parallel to an inflowing mediumxe2x80x9d.
The same Japanese patent application laid-open No. 9-503311 recites that xe2x80x9cWhen manufacturing the device, it is important to bond a surface of the sensor element into the notch such that it becomes, as far as possible, the same face as a surface of the sensor support body. This is because even if a smallest displacement owing, for example, to a bonding layer unevenly applied exists, it follows that a vortex flow and exfoliation region is generated, and the vortex flow and exfoliation region exerts an adverse effect on a heat extraction of the measurement resistor especially at the surface of the sensor element, so that a measurement result becomes erroneousxe2x80x9d.
However, in order to xe2x80x9cbond a surface of the sensor element into the notch such that it becomes, as far as possible, the same face as a surface of the sensor support bodyxe2x80x9d as proposed in Japanese patent application laid-open No. 9-503311, there is a problem in that a high and precise manufacturing technique is required and manufacturing efficiency is thereby decreased.
Further, in order to assure that the surface of the sensor element is the same face as the surface of the sensor support body, a further problem arises in that a precise inspection is necessary.
It is therefore an object of the invention to provide a flow measurement device, which is easy to manufacture and has excellent detection accuracy.
A flow measurement device of a first aspect of the invention has means, provided so as to act on a flow in a divided flow pipe, for forming such a flow as to obliquely impinge against a detection face of a flow-detection element, as schematically shown in FIG. 1(A) wherein a flow 12 is shown by a upper arrow slanting against the detection element face. In order to obliquely impinge the flow against the detection element, a flow passage or inner diameter of the divided flow pipe is reduced so as to form a passage-narrowest portion and in addition the pipe is bent at the passage-narrowest portion so as to form a inverted arc whereat the detection element is placed. In this structure, a flow speed maximizes at the passage-narrowest portion and a flow of an object such as a gas impinges obliquely on the element. A better performance of the flow measurement device is attained when an upstream flow passage and a downstream passage along the inverted arc wherein the detection element is placed in a middle is shaped in symmetry along the inverted arc, according to one of the aspects of the invention.
It is considered that, by this flow control means, a flow to be detected is constantly supplied to the detection face of the detection element and it follows that the flow to be detected surely flows on the detection face. In addition, it is considered as an advantage that generation of a vortex flow and exfoliation in the vicinity of the detection face are suppressed so that flow detection accuracy and flow detection reproducibility are improved.
Further, since it is considered that, in this measurement device, the flow on the detection face is stabilized, the detection face is not necessarily positioned on the same face as a flow passage face on both sides of the detection portion. In other words, this measurement device allows a step between the detection face and the flow passage face in the vicinity of the detection portion and, further, enlarges an allowable width in relative positional accuracy of the detection- element detection face with respect to the flow passage face.
Therefore, according to the measurement device of the first preferred aspect of the invention, it becomes unnecessary to bond the detection element into a notch of its support body with a lot of care, as required in Japanese patent application laid-open No. 9-503311 wherein the detection element surface and the support body surface is strictly on the same face without a step therebetween. That is, this measurement device allows forming such a step between the detection face and the flow passage face on both sides of the detection portion, which step is easily generated as an error. As a result, manufacture of the device is easy, and accuracy in dimensional and/or positional inspection of the element in the flow measurement device can be lowered without lowering the performance of the flow measurement device.
In this manner, since the flow measurement device of the first preferred aspect of the invention allows such a step mentioned above, it becomes possible to attach the detection element so as to be detachable from the divided flow pipe fixed to a main flow pipe by constituting the detection element and its support body as separate bodies or by constituting the detection element and its support body as bodies separate from the divided flow pipe. As a result, it is possible to exchange the detection element if the element has been deteriorated or contaminated by long term use.
Here, effects derived from the flow measurement device of the first important aspect of the invention are exemplified below.
(1) By forming a flow (or rather a down flow) obliquely impinging toward the detection face of the detection element according to the invention, generation of a vortex flow and exfoliation are suppressed in the vicinity of the detection face and, as a result, it is possible to obtain a stable detection property and reproducibility.
(2) Even if the detection face is not at the same level as the detection element support body surface, detection is possible. As a result, assembly of the detection element becomes easy.
(3) Because a down flow is formed, an accurate and stable detection of quantities concerning the flow, e.g., flow rate and flow velocity, becomes possible at a flow passage wall. In this case, it suffices if only a detection element surface or the detection face is exposed inside the flow passage.
(4) Since the detection of the flow rate and flow velocity at the flow passage wall is possible with a rough positional accuracy of the detection element, the detection element and the divided flow pipe can be made separate bodies, so that structures of the detection element and the divided flow pipe are respectively simplified and become easy to manufacture.
(5) It is possible to constitute a flow passage shape of the divided flow pipe in compliance with a requirement for measuring both a normal flow and a reverse flow, or either the normal flow and the reverse flow is selectively measured so as not to be influenced by the other flow, by forming the flow passage in symmetry between upstream and downstream sides with the detection element placed therebetween.
(6) Since another divided flow passage can be formed in the divided flow pipe, improvements in contamination resistance and mechanical handling property are expected.
A flow measurement device of a second aspect of the invention has a detection element which is more exposed to the flow in the divided flow pipe at a wall portion or a pipe wall of the divided flow pipe and detects a flow quantity, and means provided in the divided flow pipe for forming a flow that obliquely impinges the detection face of the detection element. According to this measurement device, the detection element and the divided flow pipe can be made as separate bodies, so that structures of the detection element and the divided flow pipe are respectively simplified and become easy to manufacture.
A flow measurement device of a third aspect of the invention has a detection element which is disposed in a portion which, in the divided flow pipe, protrudes from the main flow pipe, and detects a flow quantity. According to this measurement device, an assembly of the detection element is made easy and, further, a degree of freedom in design of the main flow pipe and its outside vicinity is improved.
In a measurement device of a fourth aspect of the invention, the detection face of the detection element protrudes from an adjoining flow passage face or from a detection element support body surface. This protrusion further improves the previously described effects, and best improves them with the following optimization linked with a fifth aspect of the invention.
In a flow measurement device according to a fifth aspect of the invention, the detection face of the element protrudes 0.05 mm to 0.3 mm from a level of an adjoining inverted arc wall face of the flow passage or the detection element support body. This protrusion range of 0.05-0.3 optimizes the effects previously described when the first and fifth aspects are combined; the reason is illustratively understood by referring to FIG. 16(A), FIG. 16(B) and FIG. 16(C). When the detection element protrudes by a protruded height (H greater than 0) as shown in FIG. 16(A), a vortex or exfoliation flow that appears along or in the detection element face is greatly reduced or substantially eliminated under the obliquely impinging flow, compared to the element face formed at the same flat level (H=0) or at a lower recessed level (H less than 0) with the adjoining inverted arc wall face formed on the support body or the divided flow pipe.
In a flow measurement device of a sixth aspect of the invention, a detection element is disposed such that the flow in a measurement object pipe (main flow pipe) is taken into a detection pipe (divided flow pipe), the flow taken into the detection pipe is abruptly changed in direction, or rather the flow is inverted at a flow-direction inverting portion formed in the detection pipe so that the flow taken into the detection pipe obliquely impinges a surface of the detection element placed substantially at the middle or bottom of the direction-inverting portion or at the downstream side including the vicinity of the downstream side of the detection element.
A flow measurement device of a seventh aspect of the invention has a divided flow pipe forming an opening or window at the direction-inverting portion of the divided flow pipe wall, and a detection element support body including a circuit board for driving or controlling the detection element and detachable from the divided flow pipe is incorporated at the opening. The detection element is disposed in the opening so that the face of the detection element protrudes 0.05-0.3 mm from an edge of the opening.
Preferred implementation modes of the invention are explained below.
In a preferred implementation mode of the invention, at the inverted or curved portion of the divided flow pipe (detection pipe), the detection face of the detection element is exposed inside the divided flow pipe. More preferably, a curved pipe (divided flow pipe) is attached in a direction orthogonal to the main flow pipe for measuring an object such as a gas, and the detection element (detection portion) is provided in such a curved portion (folded or inverted portion where a flow passage is curved) of the curved pipe. Alternatively, the detection element or detection portion is disposed in a portion where the flow in the divided flow pipe is inverted or a direction of the flow is sharply changed or in downstream position of the inverted portion including downstream vicinity thereof. Further most preferably, the detection face of the element is exposed to a portion where the flow in the divided flow pipe is fastest in its flow speed. In other words, the detection face is exposed to a portion where the flow is throttled in the divided flow pipe and in addition the flow is changed in its direction. The speed of the flow becomes highest where the divided passage defined by the divided pipe wall is narrowest and inverted. The speed of the flow turning outside is higher than that of the flow turning inside.
In another preferred implementation mode of the invention, in order to generate a flow (down flow) obliquely impinging against the detection face, the detection element is disposed in the curved portion of the flow passage where a flowing object such as gas inverts its flow direction with its highest or rather fastest speed. Since the direction of flow is necessarily changed in the curved portion, it is easy to constantly obtain the down flow obliquely impinging on the detection element. Further, in the case that the curved portion or the flow passage face in at least an upstream side of the curved portion includes a concave curved face or a convex curved face or slant face extending toward the detection portion, it is further effective for generating such down flow.
In another preferred implementation mode of the invention, from the flow introduced into a divided flow passage in the divided flow pipe, the down flow for the detection face is constantly formed by protuberances and the curved portion.
In another preferred implementation mode of the invention, a separator (partition wall) is provided in a center of the detection pipe (constituting the divided flow pipe), and the flow introduced into the detection pipe is inverted or sharply changed in its direction by the separator.
In another preferred implementation mode of the invention, as flow control means for forming a flow (down flow) obliquely impinging against the detection face of the detection element or a flow flowing obliquely with respect to the detection face, a flow passage face is present protruding at least as far as the detection face in at least an upstream or an upstream and/or a downstream of the detection element.
As the protrusion form, one capable of forming the flow obliquely impinging against the detection face suffices and, preferably, it protrudes concavely or covexly, or the protrusion surface is made into a linear, polygonal or concavely curved slant face.
In another implementation mode of the invention, a difference (H) between a height of the detection face of the detection element and a height of the flow passage face in the vicinity of the detection face along the flow direction, i.e., a step, is made xc2x10.5 mm or below, further preferably xc2x10.4 mm or below, and more preferably xc2x10.3 mm or below. The plus is a case where the detection face is higher, and the minus a case where it is lower. The difference (H) is determined based on an angle of the down flow. A reliable performance of the flow measurement device is attained when the detection face protrudes from the level of the flow passage inner face in a vicinity of the detection face, and such a step described above is made within a range of 0.05 to 0.5 mm, preferably a range of 0.05 to 0.4 mm (50-400 xcexcm), or most preferably a range of 0.05 to 0.3 mm, when a surface undulation determined by average depth of the undulation of the detection element face is as small as or less than 2 xcexcm.
Especially, in a boundary region between the protuberance and the detection portion (region where the detection element exists), a structure in which the detection face is present in a side of the protuberance flow passage face is advantageous in preventing the vortex flow from occurring in the detection face. The structure is designed so as to minimize the vortex flow in the detection face with consideration of a flow angle by which the flow obliquely impinges on the detection element.
Further, in the boundary region, by providing a gap between the protuberance flow passage face and the detection portion, it becomes possible to effectively confine a turbulent flow within the gap.
In another preferred implementation mode of the invention, the curved portion of the divided flow pipe constitutes a part of a Venturi tube.
In another preferred implementation mode of the invention, as a support body of the detection element, a plate containing a circuit board or a circuit is used. Additionally, in a back face of the circuit board or a face on which no parts of the circuit are mounted, by forming or supporting the detection element under a state that it protrudes beyond a circuit board face, an assembly of the detection element to the flow passage or the divided flow pipe becomes easy. This brings about an advantage in that a printed wiring is applied to the back face of a usual mounted circuit board and the detection element can be installed to a predetermined position on the board while being protruded. Therefore, manufacture becomes easy without using such a high level manufacturing technique. The detection element is so bonded between circuit parts disposed in high density that the detection face of the detection element is positioned strictly on the same plane as the circuit board face.
In another preferred implementation mode of the invention, it is possible to use the detection element while being mounted on the detection element support body or a circuit board support body. The detection element support body and the circuit board support body are not necessarily exposed together with the detection element to an inside of the flow passage, and rather can be positioned in a divided flow pipe outside space separated by the flow passage wall or the protuberance of the divided flow pipe. According to this form, exchange of the detection element is easy. Preferably, the divided flow pipe has a seal portion for sealing a gap between the divided flow pipe and the detection element or the support body of the detection element.
In another preferred implementation mode of the invention, the detection element and the divided flow pipe are made separate bodies, and the detection element is attached to the divided flow pipe so as to be detachable therefrom. Further preferably, the divided flow pipe and the circuit board support body for holding the detection element are made separate bodies and, at a measurement time, they are used by being mutually assembled. It is also possible to directly bond the detection element to the circuit board support body, and a concave to some extent may be provided in this support body in order to align a position.
In another preferred implementation mode of the invention, the detection element is disposed in a flow wall or the pipe wall in the divided flow pipe and, among others, in an outer wall. As occasion demands, the detection element is disposed in the flow within the divided flow pipe.
In another preferred implementation mode of the invention, the detection element is installed such that it is exposed inside a divided flow passage bypassed from a main flow passage, or inside a further divided flow passage of the divided flow passage bypassed from the main flow passage.
In another preferred implementation mode of the invention, a stagnant portion is formed in the vicinity of an inlet port and/or an outlet port of the divided flow pipe. In this manner, contamination of the detection element by fine particles and dust, etc., is prevented in high degree.
In another preferred implementation mode of the invention, a reduced diameter portion is formed in the upstream portion of the divided flow pipe. In this manner, contamination of the detection element by fine particles and dust, etc., is prevented in high degree. Further, according to the measurement device having in the downstream portion of the divided flow pipe an increased diameter portion along a normal flow direction extending from the inlet port to the outlet port, in other words, a reduced diameter portion along a reverse direction extending from the outlet port to the inlet port, an influence of the reverse flow at a normal flow measurement time is suppressed.
In another preferred implementation mode of the invention, the flow passages in the upstream side and the downstream side of the detection element are basically formed symmetrically with the detection element being made a center. According to such a device, it is possible to suitably measure both the normal flow basically flowing from the inlet port to the outlet port and the reverse flow basically flowing in its reverse direction.
In another preferred implementation mode of the invention, a sectional shape cut along a direction orthogonal to the flow direction in the divided flow pipe is any one or more of shape(s) selected from circular, semi-circular, elliptic and rectangular shapes.
In another preferred implementation mode of the invention, the detection element measures a quantity concerning a flow, at least including a flow rate and/or a flow velocity, based on temperature.